The present invention relates to a disk rotating device using dynamic-pressure type fluid bearings, for use in a disk recording apparatus which performs the recording and reproduction of signals from a rotating magnetic disk or the like.
In recent years, recording apparatus using disks and the like have increased in memory capacity and data transfer speed. This, in turn, has required disk rotating devices used in such recording devices to be capable of high-speed, high-precision rotations. As a result, disk rotating devices in which a central shaft is supported at its both ends, such as disclosed in Japanese Patent Publication No. 62-21190 and Japanese Laid-Open Patent Publication No. 62-40662, are used in disk drives.
Referring now to the drawings, examples of the above-described conventional disk drives are described. FIGS. 6, 7, and 8 show sectional views of conventional disk drives. In a first conventional example as shown in FIG. 6, there are shown a casing 21, a shaft 22 whose both ends are fixed, ball bearings 23A, 23B, and a hub 24 rotatably attached to the shaft 22 via the ball bearings 23A, 23B. A motor stator 25 is secured to the casing 21, and a motor rotor 26 is secured to the hub 24. The hub 24 is shaped into such a configuration that disks 28A, 28B, 28C and spacers 29A, 29B can be attached thereto. Reference numeral 27 denotes a top cover.
Regarding the first conventional disk rotating device having the above arrangement, its operation is described below. First, when the motor stator 25 is electrically energized, a rotating magnetic field is generated, and then the motor rotor 26 drives the hub 24 into rotation. Then the hub 24 rotates while being supported by the ball bearings 23A, 23B.
On the other hand, FIGS. 7 and 8 show sectional views of a second conventional disk rotating device. In the figures, there are shown a casing 31, a top cover 42, bearing housings 34A, 34B, a rotatable shaft 32, flanges 33A, 33B secured to both ends of the shaft 32, and bearing covers 35A, 35B. Radial bearing grooves 36A, 36B are formed on outer circumferential surfaces of the flanges 33A, 33B, respectively. Further, thrust bearing grooves 37A, 37B are formed on surfaces of the flanges 33A, 33B in contact with the bearing housings 34A, 34B, respectively. These grooves have lubricant 38A, 38B, respectively, retained therein. A hub 39 and a motor rotor 41 are secured to the shaft 32, and a motor stator 40 is attached to the casing 31. The hub 39 is shaped into such a configuration that disks 43A, 43B, 43C and spacers 44A, 44B can be attached thereto.
In this second conventional example, when the motor stator 40 is electrically energized, a rotating magnetic field develops so that the motor rotor 41 is driven to rotate together with the hub 39 and the shaft 32. When this occurs, the radial bearing grooves 36A, 36B and the thrust bearing grooves 37A, 37B pump the lubricant 38A, 38B, respectively, to generate a pressure and generate a floating force, thus making non-contact rotation.
The above-described arrangements, however, have the following disadvantages. In the first conventional example of FIG. 6, in which ball bearings are used, rolling vibrations generated by the ball bearings 23A, 23B during rotation are transferred to the casing 21, the top cover 27, and an unshown magnetic head. As a result, there would be some cases where the recording and reproduction of signals with the disks 28a, 28B, 28C could not be accomplished.
In the second conventional example of FIGS. 7 and 8, in which fluid bearings are used, vibrations from the bearings will not be generated, but the diameter of the radial bearing grooves 36A, 36B is large. As a result, there would be disadvantages such as a large friction loss of the bearings and a large power consumption of the motor. Further, another disadvantage that is assembling accuracy cannot be easily achieved.